This application claims the benefit of Japanese Patent Application No. 2004-293319, filed Oct. 6, 2004. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety.
Aspects of the invention can relate to a projector that projects an image using a light modulation device, such as a liquid crystal panel.
A projector in the related art illuminates liquid crystal panels of respective colors. Hence, a projector of a type, such as those disclosed in JP-A-11-64977, JP-A-11-38210, JP-A-2003-344804, and JP-A-2001-66694, separate a light source light from the light source into lights of three colors, and includes a relay system disposed in an illumination optical path for blue to compensate for a difference of the optical path with respect to lights of the other two colors. More specifically, a first related art projector disclosed in JP-A-11-64977 can be configured to utilize blue lights effectively by allowing the relay lens in the center of three relay lenses forming the relay system to move, for example, in the optical axis direction for scaling up and down the size of an illumination region with respect to the liquid crystal panel. A second related art projector disclosed in JP-A-11-38210 corrects a chromatic aberration for red with ease by narrowing the lateral width of a projected image for red, for example, by tilting a dichroic filter for reflecting red lights incorporated in a light combining cross dichroic prism on one side in reference to the cross line to form a convex surface. A third related art projector disclosed in JP-A-2003-344804 corrects a chromatic aberration of magnification, which is resulted from a difference of magnification of the projection lens for respective colors, by laminating lenses on the light exiting surfaces of the respective liquid crystal panels for adjusting projection magnification using the functions of these lenses. Further, a fourth related art projector disclosed in JP-A-2001-66694 corrects a chromatic aberration of magnification of the projection lens by forming chromatic magnification correction lenses integrally with the light incident surfaces of a plastic color combining prism on the sides of the optical paths for blue and red for adjusting projection magnification using the functions of these lenses.
A projector in the related art of another type, such as those disclosed in JP-A-2001-66695 and JP-A-2000-155372, separates a light source light from the light source into lights of three colors and includes a relay system disposed in the illumination optical path for red to compensate for a difference of the optical path with respect to the other two colors. A fifth related art projector disclosed in JP-A-2001-66695 suppresses the occurrence of a chromatic aberration of magnification of the projection lens by providing correction lenses between the respective liquid crystal panels and a three-color combining prism. Also, a sixth related art projector disclosed in JP-A-2000-155372 corrects a chromatic aberration of magnification of the projection lens by giving a curvature to the surface of the sandwich glass holding a wavelength film disposed between the reflective liquid crystal element and the three-color combining prism.
Further, a seventh projector in the related art of still another type, such as the one disclosed in WO94/22042, separates a light source light from a white light source into lights of three colors and includes a light guiding system, such as a relay system, disposed in the illumination optical path for green for compensating for a difference of the optical path with respect to the other two colors.
However, for the projector of the type in which the relay system is disposed in the optical path for blue, for example, because the high pressure mercury-vapor lamp is used as the light source, blue may become relatively weak in comparison with the other colors, and the projector of this type may fail to adjust a white balance appropriately. In such a case, the white balance may be achieved through signal processing such that adjusts a luminance value of an image signal that should be inputted into the liquid crystal panel. However, this raises a problem that the brightness and the contrast of an image are deteriorated. When the relay lens provided in the optical path for blue is allowed to move in the optical axis direction, it is possible to lessen a loss of blue lights whose luminance readily becomes insufficient, and wasting of an illumination light can be therefore prevented. This configuration, however, cannot positively eliminate bias of the white balance resulting from the light-emitting characteristic of the high pressure mercury-vapor lamp.
A chromatic aberration of magnification is unavoidable in the projection lens because lights diffuse in individual lenses forming the projection lens. In principle, a red light and a blue light have aberrations in the opposite directions with respect to a green light. Recently, the lens is designed to suppress a chromatic aberration of magnification using a special grinding material, and there is a projection lens in which aberrations of a red light and a blue light with respect to a green light are in the same direction. Correction on a chromatic aberration of magnification, as described above, has been proposed for such a projection lens. However, the projector that guides a blue light to the relay system has problems as follows as to a correction on the chromatic aberration of magnification. That is, in a case where the dichroic filter for reflecting a red light in the color combining prism is tilted on one side in reference to the cross line, the lateral width of a projected image for red can be matched with a lateral width of a projected image for blue. However, in a case where lateral widths of projected images for red and blue are matched with a lateral width of a projected image for green, because the projection lens has an aberration as described above, the dichroic filter for reflecting a blue light needs to be tilted on one side in reference to the cross line in addition to the dichroic filter for reflecting a red light.
The manufacturing of the dichroic prism therefore becomes more complicated, which consequently increases the manufacturing costs. Because only the dichroic filter for one color is tilted, when a chromatic aberration of magnification for one of a red light and a blue light is to be reduced, the chromatic aberration of magnification for the other color becomes to large not to be corrected by merely tilting the filter. In addition, the method of laminating the lenses to the light exiting surfaces of the respective liquid crystal panels has the need to provide special chromatic correction lenses in the optical paths for respective colors. This not only complicates the manufacturing sequence and thereby increases the cost, but also may possibly attenuate a blue light due to the presence of the chromatic correction lens.
In the method of forming a chromatic magnification correction lens integrally with the light incident surface of the plastic color combining prism, processing accuracy of plural chromatic magnification correction lenses formed for respective different color lights have to be increased to achieve sufficient accuracy. This also complicates the manufacturing sequence and thereby increases the cost.
The projector of the type in which the relay system is disposed in the optical path for red has the same problem. That is, red becomes relatively weak in comparison with the other colors, and the projector may fail to adjust a white balance appropriately. In the method of disposing correction lenses of chromatic aberrations of magnification in the optical paths of respective colors in the projector of the type in which the relay system is disposed in the optical path for red, the correction lenses have to be incorporated into plural optical paths. Moreover, the correction lenses may possibly attenuate red lights. The method of giving a curvature to the surface of the sandwich glass also has the need to give curvatures to the surfaces of sandwich glass in plural optical paths. Furthermore, red lights may possibly be attenuated.
The projector in which the relay system is disposed in the optical path for green has advantages in that intensity of green lights, which are often superfluous due to the light-emitting characteristic of the high pressure mercury-vapor lamp used as the light source, can be readily reduced, and that adjustment of color temperatures, to which the demanding level is increasing in recent years, can be performed with relative ease. However, as with the projectors in which the relay system is disposed in the optical path for red or blue, chromatic aberrations of magnification for three colors cannot be corrected easily. More specifically, in a case where chromatic aberrations of magnification for three colors are to be corrected, for example, the enlarged sizes for red and green are matched with the enlarged size for blue. In this case, however, not only the dichroic filter for reflecting red lights, but also the dichroic filter for reflecting green lights needs to be tilted on one side. This complicates the manufacturing of the cross dichroic prism and increases the cost. In the method of disposing chromatic correction lenses in plural optical paths, at least two lenses are necessary. This also complicates the manufacturing sequence of the cross dichroic prism and thereby increases the cost.